1. Field of the Invention
The invention relates to a temperature-controlled clutch filled with a viscous fluid, that is, a fluid-friction clutch. Spacings for generation of power-transmitting viscous forces are provided between a drive disk fastened on the primary (driving) side of the clutch and clutch-driven surfaces arranged on the secondary (driven) side of the clutch.
2. The Prior Art
One problem encountered in such fluid-friction clutches is that of maintaining constant the spacing between the driving and the driven surfaces for transfer of the torque. Any variation of the spacing, which is of utmost importance in relation to the viscous forces, causes the torque transmitted by the clutch to vary. Variation in the transmitted torque leads to uncontrollable and undesirable deviations from the nominal rotational velocity, both when the clutch is engaged and during idling.
Known clutches are equipped with a drive disk rigidly mounted on the primary (driving) side, from which torque is transmitted through the spacing to the drive surface of a housing on the secondary (driven) side of the clutch. In German published application No. DE-OS 27 23 429, the spacings are formed by labyrinth-like, concentrically-interacting surfaces. To assure that the effective spacings are maintained constant, dimensional tolerances must be closely held for both the driving and the driven surfaces. This is not always attainable in manufacture and assembly, and therefore a planar eccentricity of the drive disk with respect to the driven housing must be expected. This also affects the spacing between the drive disk and a pumping element arranged in a position axially offset from the driven surface on the secondary side of the clutch. To the extent that this spacing is affected, uniform pumping of the fluid is not assured and deviations from the desired clutch characteristic result during idling. German published application No. DE OS 24 07 062 discloses a similar clutch in which the spacings provided for the transmission of torque consist of theoretically plane parallel surfaces. Again, however, a variation of the spacing due to manufacture and assembly conditions leads to deviation in the transmitted torque and, thus, a resultant deviation in operation of the rotational velocity from nominal values. In this case as well, pumping by means of the pumping element axially offset with respect to the drive disk is not assured in a controllable fashion. Finally, German published application No. DE OS 25 32 201 describes a spring-loaded, axially-offset pumping element, the pumping element being pressed constantly against the rigid drive disk. While the gap between the drive disk and the pumping element has been eliminated in this arrangement, this type of clutch is applicable only up to a limited rotational velocity. If this velocity is exceeded, the resonant frequencies of the pumping element-spring system no longer permit the pumping element to be constantly pressed against the drive disk.